The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
ACK/NACK acknowledgement/negative acknowledgement
CQI channel quality indicator
CDMA code division multiple access
CSI channel state information
DCI downlink control information
DL downlink (eNB towards UE)
eNB EUTRAN Node B (evolved Node B)
EUTRAN evolved UTRAN (LTE)
FEC forward error coding
IC interference cancellation
LTE/LTE-A long term evolution/long term evolution-advanced
MCS modulation and coding scheme
MIMO multiple input multiple output
MU-MIMO multi-user MIMO
PDCCH physical downlink control channel
PDSCH physical downlink shared channel
QAM quadrature amplitude modulation
QPSK quadrature phase shift keying
RRC radio resource control
RV redundancy version
RX receive or receiver
SINR signal to interference plus noise ratio
TB transport block
TBS transport block size
SU-MIMO single user multiple input multiple output
TX transmit
UE user equipment
UL uplink (UE towards eNB)
UTRAN universal terrestrial radio access network
Non-orthogonal access schemes are being considered for radio access technologies known currently as “beyond 4G1”, or B4G, which is targeted for commercial deployment in 2020. Such access schemes may also be deployed in more near-term evolutions/releases of the LTE/LTE-A radio access technologies. Non-orthogonal access is considered as a potential multiple access scheme to significantly increase the downlink capacity that can be offered to cell edge users. There are several ways to realize improved capacity from non-orthogonal access techniques depending on the scheduler algorithms used by the eNB. FIG. 1 illustrates the general principle which is based on path loss separation of users nearer the center of the cell which are considered to be the users with stronger signal strength, and users nearer the edge of the cell which are considered to be the users with weaker signal strength. This is a simplification in that signal strength is not always directly related to distance from the transmitting entity, but for purposes of explanation nothing is lost from this simplified radio environment.
FIG. 1 is an exemplary radio environment in which an access node, such as for example an eNB of an LTE-A system, transmits to user equipments/mobile terminals grouped for the sake of explanation into cell center users and cell edge users. For non-orthogonal access, the eNB will allocate more resources to cell edge users, at the expense of resources available for the cell center users. In an extreme case the eNB may give all its resources to the weakest user at the cell edge.
The principle of non-orthogonal access is known in the art. For example, non-orthogonal access can be realizes by superposition coding (for example, with non-orthogonal CDMA scrambling/spreading), by hierarchical modulation which uses layered modulation of base and enhancement layer symbols, by multilevel coding which uses several error correcting codes with different capabilities, and/or by dirty paper coding which introduces precoding to cancel the effect of interference known to the transmitter.
As a specific example to illustrate the radio environment, consider that a weakest cell edge user and a strongest cell center user both get transmissions from the eNB. Assume the eNB transmits with QPSK modulation to that weakest user with transmit power Sw, and that the eNB transmits to the strongest user with superposed QPSK/QAM modulation and transmit power Ss. From the perspective of the weakest user, power Ss is seen as additional interference to it. But the weak user's reception condition does not suffer much if Ss/Sw is less than SINRw. In non-orthogonal access the weakest (cell edge) user additionally benefits from additional resources as compared to the strongest (cell center) user. From the perspective of the strongest user, it also receives the eNB's transmission which is intended for the weakest user. Because the strongest user receives that transmission with good SINR it can easily decode and cancel that signal intended for the weakest user, and so this interference to the strongest user is manageable.
But non-orthogonal access requires the possibility for the eNB to allocate the same resource to multiple users. A similar same-resource scenario exists in the downlink for LTE systems where multi-user MIMO is in use. However, there is no support in LTE for a UE which is capable of intra-cell interference cancellation (IC), which is the scenario above where the strongest user decodes and cancels the signal intended for the weakest user.
What is needed in the art is a way to facilitate in practice intra-cell IC which is currently not supported by LTE radio systems. For a more practical application such improvement should also enable non-orthogonal access to be implemented in a cell where legacy UEs which do not support intra-cell IC might also be operating.